RGB (Red, Green, Blue) color space, especially the one with 24-bit true color, is used in virtually every computer system as well as other applications such as television, video, etc. For display on RGB displays, images resulting from a higher precision capturing or processing system must be quantized into RGB signals of the same quantization levels of the display. The traditional true color display with 8-bit precision in each channel can display about 16.7 million colors. Although, based on research in color science, human eye can only distinguish around 10 million different colors under optimal viewing condition, the true color display is still not detailed enough for human vision perception.
This is mainly because of the non-uniformity, in the sense of human perception, of the RGB space. The non-uniformity leads to the result that in some regions of the RGB color space the different colors are perceived the same and in some other regions the colors jump by more than one JND (just noticeable difference). For quantization in the regions where colors jump by more than one JND, the quantization error is noticed by human visual system. At the same time, human visual system is much more sensitive in luminance than in chrominance. Research shows that the human eye can discern approximately 463 different gray scales, which is about 9-bits, while it can only distinguish about 150 different hues and 50 different saturation levels.
The above two properties (i.e., the non-uniformity of RGB space and high accuracy of luminance discernment), can be checked easily using an 8-bit grayscale ramp image. The traditional 24-bit true color display can display 255 different shades of grayscales with perceivable banding artifacts. When the display is made brighter, lack of bit-depth makes the banding artifacts more obvious between neighboring shades of gray scales in 24-bit displays.
The fact that human vision is much more sensitive in luminance than in chrominance, makes it possible to manipulate the quantized color signals to preserve higher precision of luminance while keeping the difference of the chrominance signals within a tolerable range.